An effect of cation's cyano group on interactions between organic solutes and ionic liquids elucidated by thermodynamic data at infinite dilution

Abstract

New measurements on infinite dilution activity coefficients (γ∞) of 48 molecular solutes (including: alkanes, alkenes, alkynes, aromatics, ethers, alcohols, ketones, pyridine, thiophene, acetonitrile and 1-nitropropane) in 1-(3-cyanopropyl)-3-methylimidazolium dicyanamide ionic liquid (IL) are reported in temperature range from T=(308.15 to 368.15)K and addressed to previously published data. Relationships between the chemical structure of the solute and the observed value of γ∞, closely related to relative strength and nature of molecular interactions, are elucidated by the data and discussed. An effect of substitution of methyl group by cyano functional group in the cation's side chain is analyzed based on a comparison of the measurements with the data published previously for a “plain” counterpart of the studied IL, namely, 1-butyl-3-methylimidazolium dicyanamide. Besides, infinite dilution selectivity is adopted to evaluate the IL under study as an entrainer for common separation problems. Three modeling approaches are demonstrated to be capable of capturing the substitution effects observed experimentally. First, representation of the investigated systems by linear solvation-energy relationship (LSER) is shown and an effect of cyano group is confirmed in terms of the coefficients of the obtained correlation. Hildebrand solubility parameters of pure IL are calculated by regressing the γ∞ data with regular solution theory in order to check an influence on enthalpy of vaporization. Finally, conductor-like screening model for real solvents (COSMO-RS) calculations is demonstrated along with a discussion of an impact of molecular geometry of cation and solute on the accuracy of predicted γ∞ data.